This invention relates to organometallic compounds comprising a Group 4-6 transition metal compound in which the metal is in a reduced oxidation state and which when activated by cocatalyst compounds, are suitable olefin polymerization catalysts.
Coordination polymerization of olefinically unsaturated monomers is well known and has led to the great proliferation of thermoplastic compositions of matter from olefins, such as polyethylene, polypropylene, and ethylene propylene rubber. Early pioneers utilized the early transition metal compounds, particularly those of the Group 4 metals, with such activators as aluminum alkyl compounds. Later developments extended this work to bulky ancillary ligand-containing (e.g., xcex75-cyclopentadienyl) transition metal compounds (xe2x80x9cmetallocenesxe2x80x9d) with activators such as alkyl alumoxanes. Representative work addressing polymer molecular weight effects of substituted mono and bis metallocene compounds is described in EP-A 0 129 368 and its counterpart U.S. Pat. No. 5,324,800. Hetero-atom containing monocyclopentadienyl metallocene compounds are described in U.S. Pat. No. 5,057,475 and silicon bridged biscyclopentadienyl metallocene catalysts are described in U.S. Pat. No. 5,017,714. Recent developments have shown the effectiveness of ionic catalysts comprised of activated metallocene cations stabilized by compatible noncoordinating anions, see for example U.S. Pat. Nos. 5,278,119 and 5,384,299 and WO 92/00333, each of which is incorporated by reference for purposes of U.S. patent practice.
Transition metal polymerization catalyst systems from Group 5-10 metals wherein the active transition metal center is in a high oxidation state and stabilized by low coordination number polyanionic ancillary ligand systems are described in U.S. Pat. No. 5,502,124 and its divisional U.S. Pat. No. 5,504,049. Suitable low coordination number polyanionic ancillary ligands include both bulky imides and carbollides. Such are said to be suitable alone or in combination with conventional monoanionic ancillary ligands, such as cyclopentadienyl derivatives. Example 1 illustrates tris(pyrazolyl)borato vanadium oxide dichloride, a d0 vanadium compound, and ethylene polymerization with it. Reduced Group 4-6 transition metal complexes useful as polymerization catalysts are described in WO96/13529. These complexes comprise a multidentate monoanionic ligand and two monoanionic ligands, optionally with extra ligands. Each example illustrates the use of titanium complexes having a cyclopentadienyl ligand.
Hydrotris(pyrazolyl)borate is an art recognized ligand for organometallic compounds and its use for d0 compounds suitable as catalysts have been described. See, for example, WO 97/23492 describing bidentate tris(pyrazolyl)borate ligands on metals from Groups 8-10 used for low molecular weight polymers, and WO 97/17379 describing specifically substituted pyrazolyl containing ligand systems for transition metals, the examples illustrating primarily d0 compounds of Group 4 metals. U.S. Pat. No. 5,312,794 describes ring opening metathesis polymerization of cyclic olefins using catalysts with a hydrotris(pyrazolyl)borate derivative of molybdenum and tungsten in the +4 or +5 oxidation states. With few exceptions, the use of tris(pyrazolyl)borate (xe2x80x9cTpxe2x80x9d) complexes as catalysts involves d0 metal centers, as noted. The only prior art exemplifying a non-d0 metal complex, WO 97/17379 in comparative example 12, shows such to have extremely low activity and to be essentially ineffective.
Additional catalysts would be desirable to supplement the above described technology, particularly those suitable for use as insertion polymerization catalysts for olefins.
This invention is directed to reduced oxidation state Group 4-6 metal compounds, (those having d1-d3 electron configurations) preferably the first row metals in those groups, suitable for activation as polymerization catalysts and characterized by comprising a substituted tris(pyrazolyl)borate ancillary ligand and a plurality of single or multidentate uninegative ligands, excluding cyclopentadienyl ligands and at least one neutral obner group. The invention includes a polymerization process characterized by comprising contacting one or more monomers polymerizable by coordination or insertion polymerization under suitable polymerization conditions with these catalyst compositions.